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Thread: proportioning valve

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    proportioning valve

    hi guys n ladies to remove the stock proportioning valve on the brake master cylinder do you take out the spring and its done or do you need to cut off the male phallic bit on the inside of the bolt that compresses the spring? tia
    Last edited by marklee77; 15-07-2019 at 21:49.

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    Guest immy21's Avatar
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    If your BMC is the internal/front proportioning type, then shim the spring until it's nearly coil bound when refitting the bolt. Done 3 BMC's this way, current one tested with brake pressure gauges, pressure rose and peaked evenly, then stuck on an external prop valve.

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    hi immy thank you for your reply yes my bmc is the internal front type I have done this and I am still locking the fronts way to early how many shims did you useand what were there total thickness? I need to work out why shimming my bmc made no difference is it possible to just remove the whole valve?
    Last edited by marklee77; 16-07-2019 at 21:22.

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    Guest immy21's Avatar
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    Quote Originally Posted by marklee77 View Post
    hi immy thank you for your reply yes my bmc is the internal front type I have done this and I am still locking the fronts way to early how many shims did you useand what were there total thickness? I need to work out why shimming my bmc made no difference is it possible to just remove the whole valve?
    This many:

    Quote Originally Posted by immy21 View Post
    I leave the spring in, add washers between the bolt and spring until the bolt won't fully seat, then remove one shim and your good. iirc 4 shims meant the bolt wouldn't fully seat so for me 3 shims was good. Carefull not to damage threads when putting bolt back in as the spring tension will be strong.

    I have a spare rebuilt and shimmed up BMC, I'l open it up and double check for you.
    You have 350z front's and standard rears, I don't know what pads you have. Ignoring pads, you are way under braked at the rear, upping rear pressure alone will not fix it.

    I would suggest upgrade your rear hardware, at the bare minimum match the fronts (Calipers, discs and pads) ideally over brake the rear and back it down with the prop valve.

    Edit: To answer your other question
    Removing the valve in theory should equalise the front and rear, however if you have a leak, you lost all brakes. Retain the valve, front or rear brakes will still work independently if you loose one of them, for safety I wouldn't remove the valve.
    Look I'v chased my tail before thinking it's a brake pressure issue, brake pressure gauges confirmed I was wrong. Simply rear was under braked.
    Last edited by immy21; 17-07-2019 at 00:19.

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    hey buddy I did not realise it was you who helped me last time with this I think I am gonna have to whack 350z calpiers and disks on the rear, what are brakes are you running?

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    Guest immy21's Avatar
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    My current car is an S15r, really it's just a rarely used fast road car with very occasional grip track:
    R33GTR front calipers, Z32/Skyline rear, Project MU HC800+ all round, Shimmed BM50 with Tilton Prop valve set to full rear, ABS retained and road tyres. I would say it's still a bit under braked at the rear.
    Since I had all 4 calipers professionally refurbed, I'm leaving it as is for now, with the possibility of a bigger rear disc with adaptor brackets.
    Brakes are decent but nothing special.

    My last car, the S14a in my avatar did do a reasonable amount of grip track as well as fast road and drift track, I had:
    R33GTST front and rear calipers, Carbon Lorraine RC5+ all round, shimmed BM57 with Willwood prop valve a bit less than full rear (too much rear gave snap over steer braking and steering), no ABS, front ducts, road tyres.

    This was such a beautifully balanced setup, trail braking on track was a joy, still undersized though.


    One thing I found with all my testing was adding rear brake significantly decreased overall stopping distance/outright braking power before the fronts would lock.
    Last edited by immy21; 17-07-2019 at 23:03.

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    both cars sound nice love the rc5 how come you sold the s14? thats very interesting what you say about stopping distance cause I can feel on track the car will stop quicker with more rear grip plus Ive flat spotted my tyres on track then have wheel wobble with abs removed its too easy to look up and I can feel theres room for improvement even with my ap prop valve set to the max. I think I am gonna go with 350z on the rear cause thats whats up front did the bm57 make a big difference? and is it shimmed the same way as the the standard s14 bmc? is there an even more powerfull bmc? like you said idealy I would like too much rear bite that I can then dial out with the prop valve

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    Guest ps13ben's Avatar
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    I must admit this thread has been a very interesting read indeed,
    I have a set of R33 calipers front and rear with RC5s up front and was getting the fronts to lock wayyyy too easily when braking so was also looking into a proportioning valve.
    I didnt know about the OEM unit in the BMC though so thank you IMMY for that, it makes perfectly good sense.
    i have recently fitted a BM57 going from a BM44 there is a bucket load of difference with the pedal being loads firmer and there is a slight increase in front/rear balance but needs a good bit more i feel.

    The RC5 pads are jesus's testicles if you can live with the noise, lovely bits of kit and night and day in difference

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    BM57 for any upgraded calipers IMO. I ran AP Racing 6 pots up front and R33 GTR Brembo on the rear and didn't realise how bad it was until I switched to the BM57

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    Guest immy21's Avatar
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    Quote Originally Posted by marklee77 View Post
    both cars sound nice love the rc5 how come you sold the s14?

    UK car, shell was rotten, some drift track wounds, just felt like a waste to keep putting money into it so broke it for parts and planned to import an FD RX7, boat turned up with a S15r
    I should have kept the S14a, cared less about it and just enjoyed it Got an MX5 for the drift track now.


    thats very interesting what you say about stopping distance cause I can feel on track the car will stop quicker with more rear grip plus Ive flat spotted my tyres on track then have wheel wobble with abs removed its too easy to look up and I can feel theres room for improvement even with my ap prop valve set to the max.

    Simple test for anyone, try a brake test from reasonable speed say 60ish, then do another while smoothly applying handbrake, don't lock obviously, the difference is fairly dramatic. In the real world though bumps and turns does reduce the amount of rear we can use, less weight transfer from our stiff cars increases the rear we can use.

    I think I am gonna go with 350z on the rear cause thats whats up front did the bm57 make a big difference?

    In theory bigger BMC means pedel will feel shorter/sharper and harder, Smaller BMC longer/progressive and softer pedal, having tested BM44/BM50 and BM57 on my S14a, that's what I felt. Going with bigger piston calipers has the opposite effect of smaller BMC, longer softer pedal.
    Brembo calipers do have bigger pistons. Rear s14 single piston and non Brembo twin piston have the same effective piston area due to sliding caliper v rigid caliper design. Willwood brake calculator confirms this.
    In reality, well, sometimes you just gotta try it out for yourself and see what you prefer, I know ABT is a strong advocate for a BM57, I'm happy with the modulation of BM50 but still might end up with a BM57 on my S15 to try out.
    How are you going to fit the 350z rear caliper?

    and is it shimmed the same way as the the standard s14 bmc?
    My S15 BM50 is, can't remember for stock S14 BMC as the first BMC I shimmed and fitted was BM57

    is there an even more powerfull bmc?

    Over size the BMC and the pedal will get hard and too sensitive to modulate, soften it with bigger servo but then it's even harder to modulate (Auto servo give more assistance). I haven't tried different servo and bare in mind I only had BM57 with Nissan calipers, I'v not tried BM57 with bigger piston Brembo's. BM57 is the safe option.
    like you said ideally I would like too much rear bite that I can then dial out with the prop valve
    New HFM BM57

    https://www.ebay.co.uk/itm/BM57-Brak...-/152878553273

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    bm57 is going on the shopping list then there are 2 versions abs and non abs what are your thoughts on this my abs is deleted and have made hard lines to all 4 corners direct from the master

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    thank you had this page open for a long time b4 repling so had not read your post even thought it is posted after your reply

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    https://www.ebay.co.uk/itm/HFM-BM57-...8AAOSwx2hdNtP9

    non abs?
    ##just read the decsription saying for abs and non abs I am going to get it just asking about the 3 ports before buying it presume 2 for the front right and left and one for the rear
    Last edited by marklee77; 24-07-2019 at 00:27.

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    Guest immy21's Avatar
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    Yeah non abs then, as you said 2 ports for the front one for the rear.

    Since they claim to manufacture the BMC, I would suggest tell them you have an external prop valve and don't want the rear being limited. It will be interesting to see how they deal with it.

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    that's correct, 2 for the front and 1 for the rear.

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    hey guys taken a while to get these bits, but I finally got rear 350z brembos, r33 handbrake cables, r33 backing plates, r33 drum mechanisum, 370z rear disks, pads, adapter brackets and a new nissan bm57 1/16 I undone the prop valve and its totally different to the bm50 theres no spring for starters does anyone have any experience of this? I looked on line the split point is a lot more rear biased but idealy I would still like to set it up with too much rear bias that I can the dial back with the prop valve any ideas?

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